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Is a Brand-Name Fluoroelastomer the Same as FKM?
Not exactly: Viton® is a registered trademark for the FKM polymer families of one maker, Chemours, which took the brand over from DuPont. FKM is the ASTM D1418 designation for the whole class of fluorocarbon elastomers, whichever company made the polymer. Every Viton part is an FKM part; an FKM part is a Viton part only if the polymer came from that maker.
The names and who defines them (ASTM D1418, ISO 1629)
| Name | What it means | Who defines it | Where you see it |
|---|---|---|---|
| FKM | The fluorocarbon (fluoroelastomer) rubber class | ASTM D1418 | ASTM D2000 HK callouts, datasheets, most North American prints |
| FPM | The same class under the ISO naming | ISO 1629 | European prints and datasheets |
| Viton | A trademark for the FKM polymer families of one maker | Chemours | Prints that name a brand, legacy drawings, catalogs |
| Fluoroelastomer | The generic chemistry word | Trade usage | Catalogs and datasheets |
| AMS7276, AMS-R-83248 | Aerospace material specifications an FKM compound is qualified to | SAE | Aerospace prints and qualified parts lists |
A print that says FKM, FPM or D2000 HK is naming a class, and any qualified compound in the class meets it. A print that says Viton is naming a polymer source, and the part is expected to be molded from that maker's polymer. The AMS7276 guide and the M83248 guide cover the aerospace documents in the last row.
What is the same
The chemistry is shared. FKM polymers are copolymers or terpolymers of vinylidene fluoride with hexafluoropropylene, and in the terpolymers tetrafluoroethylene as well, and the fluorine on the polymer backbone is what gives the class its heat and fuel resistance. The Parker O-Ring Handbook lists the class at -26 C to 204 C (-15 F to 400 F), with low-temperature grades to -46 C (-51 F); those figures apply to a Viton compound and to an unbranded FKM compound alike.
The media profile is shared too: petroleum oils, fuels, aromatic and chlorinated solvents, acids and ozone are the class's strengths, and hot water, steam, ketones, amines and glycol brake fluid are its weaknesses. The temperature guide and the chemical compatibility guide give the class figures, and the FKM and Viton material page the compounds supplied.
What can differ
| Family | What changes | Typical use |
|---|---|---|
| Copolymers (the general-purpose grades) | Vinylidene fluoride and hexafluoropropylene; the base grade, sold by the brand owner under its A family | Most O-rings; ASTM D2000 HK callouts |
| Terpolymers | Tetrafluoroethylene added, more fluorine on the backbone, better resistance to solvents, acids and heat; the B and F families | Chemical process, fuel systems, oxygenated fuel blends |
| Low-temperature grades | A perfluoromethyl vinyl ether monomer in place of hexafluoropropylene keeps the compound flexible at lower temperatures; the GLT and GFLT families | Aerospace, cold starts, outdoor hydraulics |
| Base-resistant grades | A propylene-containing backbone that tolerates amines, steam and hot water the standard grades cannot | Oilfield, some process equipment |
| Specialty blends | Multi-monomer grades for base and sour gas resistance | Downhole and sour service |
The compound matters as much as the polymer. Two 75 Shore A fluorocarbon compounds from different molders can differ in compression set, low-temperature retraction and color, because the filler, cure system and process are the molder's. The datasheet and the specification, an ASTM D2000 line callout or an AMS document, are what qualify a part; the brand name alone qualifies the polymer. The durometer guide and the compression set guide cover the two figures that differ most between compounds.
Writing the callout
The print governs. When it says Viton, the part is quoted as Viton polymer and the question of whether an unbranded FKM is acceptable goes back to the drawing owner, with the answer recorded on the print or the purchase order, never assumed at the quote. When it says FKM, FPM or an ASTM D2000 HK callout, any qualified compound in the class meets it, and the material certification names the compound. When the part is aerospace, name the AMS7276 or AMS-R-83248 document and the part number, because the specification carries the qualification.
Comparisons with the other families are in the FKM and silicone, nitrile and FKM and EPDM and FKM guides, and the measuring post covers identifying a ring when the print is missing.
Viton or FKM on a quote
Conquest supplies O-rings in both: Viton polymer compounds when the print names the brand, and FKM compounds to ASTM D2000 or the AMS document when it does not, with the material certification naming which one shipped. A ring that failed in service is read the same way whichever name is on the print; the failure modes post separates a compound problem from a gland problem.
Viton and Teflon® are trademarks of The Chemours Company; no affiliation or endorsement is implied.
Sources
- ASTM D1418, Standard Practice for Rubber and Rubber Latices, Nomenclature; ISO 1629, Rubber and latices, Nomenclature (titles only)
- FKM, Wikipedia (the five chemistry types of the class and the Viton trademark's move from DuPont to Chemours), read 2026-09-14; the family letters are as Parker and the trade catalogs print them
- Parker O-Ring Handbook ORD 5700 (2018), section 2.2, the FKM temperature band and media profile, read 2026-09-14
- SAE AMS7276 and SAE AMS-R-83248 (titles only)
Frequently asked questions
Can generic FKM be substituted for Viton?
Only with the drawing owner's approval recorded on the print or the order. The chemistry is the same class, but a brand on the print is a source requirement, and it is the buyer's call to relax it.
Is Viton still made by DuPont?
No. Chemours has owned the Viton business and trademark since it was spun out of DuPont in 2015. Drawings that say DuPont Viton mean the same polymer families.
What does FPM mean on a European print?
The same material class as FKM, named under ISO 1629 instead of ASTM D1418.
What does ASTM D2000 HK mean?
A rubber classification band: type H for the heat resistance level and class K for the oil swell level. Fluorocarbon compounds fall in it, so HK on a print means an FKM class part without naming a brand.
Is Viton the same as Teflon?
No. Teflon is a trademark for PTFE, a fluoroplastic that does not stretch and is not an elastomer. Viton is a fluoroelastomer, a rubber.
Does an FKM O-ring work in steam?
The standard grades do not; hot water and steam attack them. EPDM is the usual steam elastomer, and only specialty base-resistant FKM grades are rated for it.
Related guides
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